I really dislike to rebuild system databases, thus I will have a file backup of the system databases (database and log). In the case of such a scenario that you describe, I would copy inn the file backup, start in single user mode, restore the lastest database backups, and voila, the system is up and running. Just keep in mind to update the file copy whenever the system is upgraded.

And the best of all, with this method you don't have to reapply service packs and patches.